1. Field of the Invention
The present invention concerns a hydraulic control system of an automatic transmission for a vehicle.
2. Description of Prior Art
The automatic gearshift of a vehicle is carried out by selectively associating the friction elements such as clutches, brakes, etc. with the sun gears, planetary gears, and ring gears of the planetary gear units. To this end, a transmission control unit TCU is provided to control such association. The power train of the automatic transmission generally employs a one-way clutch for providing a rotational member with a reaction force under the control of the hydraulic control system.
However, such one-way clutches are designed to perform the gearshifts in sequence very limiting the shifting responsiveness. Namely, it is impossible to make a skip shift from the third to the fifth speed or vice versa, which delays the shifting responsiveness. Besides, the one-way clutches complicate the structure of the power train.